Fire erupts at Flight 93 National Memorial in Pennsylvania

Fire erupts at Pennsylvania's Flight 93 Memorial. (Earthcam.com via CNN)

(CNN) -- A fire erupted Friday at the headquarters of the Shanksville, Pa., memorial to United Airlines Flight 93, which crashed on September 11, 2001, officials said.

"There is a potential for 9/11 memorabilia loss due to a fire," according to a statement from the National Park Service, but the extent of the damage is not known yet.

NPS spokesman Mike Litterst said 10% of the archives and museum collection was stored in the damaged buildings, but much of it was kept in a fireproof safe.

Among the items in the damaged buildings was a U.S. flag that flew over the U.S. Capitol on the day of the terrorist attack. The flag was given to the Flight 93 National Memorial last September 11. Its status was not known.

Four buildings were damaged, the park service said. Heavy rain helped the firefighting efforts.

Seven fire companies responded to the blaze, which started about 3 p.m., said Geraldine Budzina, a Somerset County dispatcher. No injuries were reported.

"I think stuff has been lost"

Ken Nacke, whose brother Louis was on Flight 93, said many 9/11 artifacts -- including notes and other mementos left at a temporary memorial at the crash site -- were being stored in the area where the fire burned.